If you have the cash to blow and you want to, why not?
I wouldn't expect huge performance increases, however. Photozone has some fairly rigorous lens tests, they're not ranking significantly higher than other good glass wide open and most lenses are pretty good by f/4 or f/5.6 anyway. Film is less demanding than digital, I doubt you could blind-test against another good lens at higher than random accuracy. The placebo effect is HUGE here, on some level your brain tries to search for something, anything to justify why the luxury (read: "better") product is better and deserves its price tag.
For example, take the Distagon 35/2. It's a $1200 lens that is matched pixel for pixel by a $400 Samyang 35/1.4. The Samyang develops essentially the same resolution as the Distagon at f/2, acceptable bokeh, plus you get a brighter viewfinder, more accurate focusing, and the capability to go to f/1.4 if you need it. Yeah, it's a bigger, heavier lens but the image is everything, right? Are there enough differences to drop 3x the price on the name-brand?
That said, there are still gems in the Zeiss lineup. Their 100mm Makro Planar is great from what I've seen. On the other hand, kind of hard to justify that kind of price tag when I can pick up a Nikkor 105/2.5 for $150 that's also razor sharp and all that jazz. If it was good enough for 50 years of Nikon professionals, it's good enough for whatever I can throw at it.
Last edited by PaulMD; 03-25-2013 at 07:23 PM. Click to view previous post history.